Kanger T3 replacement coil problem

I've only had my Kangers for about a week and I've finally clogged up one of the coils enough to try a replacement (the old one is soaking in scotch to if that unclogs it). I got both the T3s and replacement coils from vapeking. I noticed after putting it on that it rocks a bit when I screw it onto my sigelei ZMAX v2. To stop it I have to screw on really tight which I don't like to do because then when you take it off you end up unscrewing the tank from the coil part instead of the coil from the battery. I've just been tightening until it's snug but no further. More annoying that this is that it seems to be a bit hit and miss whether it will fire. When I press the button on ZMAX the display shows the voltage same as when it fires properly. I took the whole thing off and tried again and it seems the ZMAX does that even if there's nothing connected. So I'm thinking perhaps there's some mismatch in the EGO threads and it's barely making contact? I've read the ZMAX v1 had this problem but was supposed to fixed in v2 I thought. I tried putting a 510-ego adapter in between the ZMAX and the Kanger base but still got the rocking problem and the hit and miss electrical contact. I've also tried all of the above with two seperate replacement coils in case one was a dud, same deal.

Are these replacement coils genuine kanger coils? Is there something obvious I'm missing? Any ideas on how I can fix this problem appreciated.

BTW I've noticed that misfiring sometimes happens when the battery gets really low (3.4v or lower). Battery is currently reading 3.8v so I don't think that's the cause. I've only got the ZMAX set to 3.7v

I pulled the post on the T3 and it's still doing it. So I tried my vapeonly mega BCC and after some hard vaping got the same problem. The ZMAX is only 2 weeks old and the contacts look clean. I *think* it tends to happen when I'm having several draws in a row and on one of the later draws. Is it possible the battery itself is cutting out due to too much current draw?

I also notice that when it's cold I have to hold the button for a second or two before it fires. It's more than the coil warmup time. It's definitely longer than when I first started using the zmax/t3 combo.

I've got 2 trustfire 18650s and the 2 that came with the ZMAX. Seems to happen with both. I do have an Efest 18650 2200mah IMR Battery and two Efest 18350s coming in my next vapeking order (apparently both are high drain) so I guess I'll see if that makes any difference.

The other thing I've noticed is when it cuts out the T3 becomes a little to harder to draw on until it cuts back in. Any ideas what that's about? Even if there's not vapor I can tell when it's cut out because there's no hissing noise.